In a CDMA mobile communication system composed of each of a plurality of cells existing in a divided service area, in the case where a deterioration occurs in received quality at a base station or a mobile station in current communications, the method has been adopted conventionally to improve a received quality by executing DHO Between Cells with a base station in a peripheral cell.
A radio communication system in conventional DHO Between Cells is explained. FIG. 1 is a block diagram illustrating a CDMA mobile communication system.
It is assumed that mobile station MS is moving along almost halfway between first cell#1 and second cell#2. At this time, each of base station BS#1 and base station BS#2 respectively directing each cell communicates with mobile station MS under Hand-Over Between Cells condition, and transmits a information signal and a control signal obtained by communicating with mobile station MS respectively at base station BS#1 and base station BS#2 to control station MCC.
Control station MCC decides a base station after Hand-Over on the basis of the control signal from base station BS#l and base station BS#2, then obtains a certain information signal. However it has been a problem conventionally that a control station can not exactly decide a base station after DHO Between Cells even by executing DHO Between Cells on the basis of a CRC signal (Cyclic Redundancy Check) that checks data error in a control signal.
FIG. 2 illustrates frame diagrams at control station MCC in DHO Between Cells on the basis of a CRC signal checking data error in the control signal respectively transmitted from base station BS#1 and base station BS#2 to control station MCC. In FIG. 2, in the case where a CRC signal of a base station is OK and a CRC signal of another base station is NG, for instance, as shown in the frame number 1 (FRN#1) and the frame number 2 (FRN#2), control station MCC can decide a base station after DHO Between Cells simply. On the other hand, in the case where CRC signals of both base stations are both NG signals, for instance, as shown in the frame number 3 (FRN#3) and the frame number 9 (FRN#9), control station MCC can not exactly decide a base station after DHO.
For control station MCC to exactly decide a base station after DHO, methods using information such as reception level, frame error rate, bit error rate, etc. have been conventionally applied. Concretely, in a method using reception level, a base station transmitting a high reception level is selected as a base station after DHO. However it is difficult to exactly decide a base station after DHO on the basis of the above information because there is a case that control information is exactly obtained even when a reception level is low.